The present invention is directed to a novel implant and to a novel method of treatment related thereto.
In particular the invention relates to a threaded implant intended to be screwed into bone, preferably in the maxilla or mandible as a means of attaching or anchoring a prosthesis.
Current implant design, e.g. dental implant design, has tended be increasingly adapted towards different clinical situations such as placement in soft or hard bone, for example, a certain type of implant may be used for fixing into trabecular or poor quality bone, e.g. soft bone, whereas a different implant may be used for fixing into dense cortical bone or hard tissues. However, there are common features that would be desirably incorporated in an implant design placed in hard bone, like good cutting efficiency and low friction in order to have acceptable level of insertion torque. Meanwhile, there are reasons to have a high insertion torque in situations with soft bone in order to increase the initial stability by additional bone compression. Current systems available to, for example, dental practitioners do not readily lend themselves to these contradictory requirements.
The result of this trend is that there are current implant systems that have separate designs for these situations. One example is the Mk III-implants in the Branemark system (available from Nobel Biocare), which are mainly designed for use in hard bone. Similarly, the Replace system (also available from Nobel Biocare) is specifically designed for use in socket replacement. Alternatively, the Mk IV-implants in the Branemark system (available from Nobel Biocare) are specifically designed for use in soft bone. From this it can be seen that conventional systems utilise a range of types of implant designs for different types of bone quality.
U.S. Pat. No. 5,427,527, to Niznick, et al describes a dental implant system utilising a threaded cylindrical form provided with a plurality of longitudinal channels. In particular, the implant is a conical or tapered threaded implant, that is a lower part of the implant being smaller in diameter than the cylindrical bore hole and the upper part being greater in diameter. More specifically, Niznick describes a method of fixing an implant wherein the diameter of the bore hole is less than the diameter of the implant. However, one particular disadvantage of the Niznick system is that the lower part of the implant is smaller in diameter than the bore hole used, whilst this may make insertion easier, the fixture of the implant has only-limited stability.
U.S. Pat. No. 5,902,109, Reams, et al, describes a reduced friction screw-type dental implant which has a non-circular cross-section, which includes a plurality of lobes and dwells such that on insertion into the bone only the lobes engage with the bone tissue allowing bone to grow into the dwells.
International Patent Application No WO 99/23970 to Björn, et al, describes the Nobel Biocare Branemark Mk-IV system hereinbefore described. Björn describes an implant system which comprises a threaded tapered implant which is provided with a tapered anchoring hole in its upper part. In particular, FIG. 2 of Björn describes an implant provided with cutting edges (5).
U.S. Pat. No. 6,099,312 describes a dental implant member which has a generally longitudinal cylindrical shape wherein the entire length of the implant is provided with double ruled grooves, preferably equidistant from each other.
U.S. Pat. No. 5,338,197 describes a tapered anchor pin for securing an artificial tooth or dental prosthesis to the bone of a patient, having a plurality of cutting flutes disposed about the periphery of a top portion of the pin. However, the pin of the prior art is tapered only to address the problem of a countersinking operation.
In addition, a commercially available implant system from Ha-Ti Dental comprises a generally cylindrical tapered implant with a longitudinal groove which is used by anchoring in a tapered hole.
Thus, it can be seen that there are a number of problems with the existing dental implant systems. Firstly, the actual use for a given design and indication is not always followed according to the product claims. This can result in incorrect treatment or even worse, a continuous maltreatment or not optimal treatment.
Clinically, inappropriate selection may lead to poor implant stability and unacceptably high bone stresses, which can lead to failure, necrosis, fracture, etc. One example is the use of the Nobel Biocare Mk IV implant in dense bone.
Furthermore, development of new products to adjust the function or clinical procedure, e.g. to allow a new indication, leads to an even greater increase in the assortment of products.
Thus, the problems concern both the function of the implants as well as the handling and ordering situation for the clinician. This design adaptation leads undoubtedly to an increase in assortment leading to higher stock levels and thus higher working capital.
Thirdly, when a cylindrical implant is manufactured a negative tolerance is commonly introduced for the diameter difference between the apical and coronal threaded portion in order to avoid the implant failing to seat during insertion in medium to hard bone but the stability will be poorer in soft bone.
Thread cutting implants have, in the past, been designed to maximise cutting efficiency by increasing the length of the cutting edge, increasing the volume of the bone chip collecting chambers and introducing relief planes in relation to the cutting edge to provide increased contact force. Clinical problems have arisen during placement of these types of implants. Such problems include poor alignment between the thread cut in bone and the cylindrical preparation hole which can lead to poor implant stability. The malalignment may result from a decrease in the circumferential threaded area due to the presence of the cutting chamber and the relief planes. The consequential result can be poor implant to bone contact manifested clinically as wobbling during placement.
Generally, when placing an implant in bone, the diameter of the lower part of the implant is less than the diameter of the prepared cylindrical bore hole. However, in order to obtain optimum stability in, for example, soft trabecular bone, for example in the maxilla, the prepared bore hole can be as small as possible and therefore smaller than the threaded portion of the implant, leading to increased bone compression a so called under preparation.
The normal clinical procedure in an alveolar ridge is to prepare a bore hole which is smaller than the diameter of the implant body regardless of the distance from the apical end. Hence the implant, engages the bone along its entire length. This procedure includes a tapered implant in a cylindrical bore, which is distinct from that described in U.S. Pat. No. 5,427,527.
There has therefore clearly been a long felt need for an implant system which can be adapted to the actual situation by design changes and/or in combination with changes in instrumentation and/or surgical procedures. An object of this invention is to provide a universal implant which is suitable for placement and achieves optimal anchorage in either soft or hard bone. This is achieved by providing an implant which is designed to reduce high levels of compressive stress by provision of a supplementary cutting feature, during and after insertion into hard bone, but is designed for increased insertion torque when inserted into soft bone in order to obtain optimum implant stability.